Temperature Compensation For RF Detectors

ABSTRACT

Compensation for an RF detector includes components having different order temperature functions. The components are combined and may be adjusted by various numbers of user-accessible terminals to provide individual adjustment for factors such as operating frequency. In some embodiments, first and second-order temperature functions are generated independently and combined to provide a polynomial function of temperature with coefficients that may be adjusted. In other embodiments, the outputs of the function generators may be more complex functions of temperature with various adjustable parameters.

BACKGROUND

Advanced data encoding and modulation techniques have made it possibleto transmit ever increasing amounts of information through radiofrequency (RF) wireless communication systems. Accurate powermeasurement and control is critical to implementing these schemes. Forexample, code division multiple access (CDMA) systems rely on a codingscheme in which multiple users occupy the same part of the frequencyspectrum, but to one user, signals from other users appear as noise. Forsuch a system to work effectively, the transmitted power levels fromindividual handsets must be controlled so that the transmitted signalsare received at the base station at about the same power level,regardless of how far each handset is from the base station. CDMAsignals also have relatively high peak-to-average power ratios. Thesecharacteristics place extreme demands on the power measurement andcontrol system.

Another transmission technique known as orthogonal frequency divisionmultiplexing (OFDM) relies on multiple orthogonal subcarriers. Eachsubcarrier has a relatively low amplitude, but since numeroussubcarriers occasionally add in phase to create very high instantaneousamplitudes, the resulting OFDM waveforms have very high peak-to-averagepower ratios.

Systems utilizing modulation schemes with high peak-to-average powerratios must often be operated in a condition known as “backoff” in whichthe output of the power amplifier is reduced to prevent distortion thatoccurs when the signal peaks exceed the linear range of the amplifier.Accurate power measurement is critical for implementing backoff controlschemes.

Several different types of detectors are commonly used to measure thepower of RF signals. They range from simple diode-detectors to morecomplex logarithmic amplifiers (log amps) and root-mean-square (RMS)detectors. The measurement characteristics of these detectors typicallyvary with temperature. For relatively low operating frequencies, thetemperature dependencies of a detector can usually be corrected by acompensation signal having a relatively simple temperature function. Asthe operating frequency increases, however, the simple temperaturefunctions become inadequate, and more complicated adjustments arerequired. FIG. 1 illustrates a prior art temperature compensationcircuit for an RF power detector. Currents I₃ and I₄ create voltagedrops across the base-emitter junctions of diode-connected transistorsQ3 and Q4. The difference between the base emitter voltages (ΔV_(BE)) isapplied as the input voltage Vi to a transconductance multiplier cellformed by Q1 and Q2. The ΔV_(BE) is multiplied by the tail current I₅ toproduce a compensation signal I_(OUT) which is taken as the differencebetween currents I₁ and I₂.

In one configuration, the circuit of FIG. 1 is arranged in combinationwith the circuit of FIG. 2 to provide a compensation signal having alogarithmic temperature function that can be used to temperature correctthe output of a log amp. In this configuration, the current I₃ is madeproportional to absolute temperature (PTAT), while I₄ and I₅ areimplemented as temperature-stable currents (also referred to as ZTATcurrents where the Z represents zero temperature coefficient). Thisparticular combination of PTAT and ZTAT currents for I₃ and I₄ creates aΔV_(BE) having the form V_(T) ln(I_(P)/I_(Z)). When this ΔV_(BE) isapplied to Q1 and Q2, the resulting output has the form I_(OUT)=I₅ tanh[ln(I_(P)/I_(Z))] which can be approximated asI_(OUT)≈I₅ln(I_(P)/I_(Z)).

The circuit of FIG. 2 includes a user-accessible terminal ADJ to enablethe user to vary the amount of tail current I₅, and thereby adjust theamount of temperature compensation based on the operating frequency. Thereference voltage V_(REF) is a temperature stable reference voltage, sothe current through R3 is also temperature stable (ZTAT) and varies onlywith the value of R_(ADJ) which the user connects to the terminal ADJ.Therefore, the tail current 15 applied to the circuit of FIG. 1 variesonly with the value of R_(ADJ). The manufacturer typically provides atable of suggested values for R_(ADJ) for various common operatingfrequencies. This type of temperature compensation scheme is furtherdescribed in U.S. Pat. No. 7,180,359 which is by the same inventor asthe present patent disclosure and is incorporated by reference.

In another configuration, the circuit of FIG. 1 is used in combinationwith the circuit of FIG. 3 and arranged to provide different types oftemperature compensation as might be suitable for other types ofdetectors such as RMS detectors. For example, if I₄ is madecomplementary to absolute temperature (CTAT) rather than ZTAT, then thecurvature of the ΔV_(BE) function is more pronounced than in the exampleabove and provides a greater amount of adjustment. Additional shaping ofthe temperature function can be provided based on the form of the tailcurrent I₅. For example, if I₅ is implemented as a PTAT current, thecurvature of the ΔV_(BE) function is even more pronounced.Alternatively, however, the tail current I₅ can be made CTAT, ZTAT, orany other function of temperature.

As with the circuit of FIG. 2, the circuit of FIG. 3 also includes auser-accessible terminal ADJ to enable the user to vary the amount oftail current I₅, and thereby adjust the amount of temperaturecompensation based on the operating frequency. In this case, however,the temperature shape of the tail current I₅ is determined by thetemperature shape of I₆. For example, if I₆ is PTAT, the tail current I₅is also PTAT. By varying the voltage applied to ADJ terminal relative tothe reference voltage V_(REF)/2, the amount of tail current applied tothe multiplier can be adjusted to provide an approximation of therequired temperature compensation for the specified operating frequency.

FIG. 4 illustrates another prior art circuit for providing temperaturecompensation to an RMS detector. The temperature dependency is providedby the junctions of Q8 and Q9. The currents through Q8 and Q9 passthrough cascode transistors Q10 and Q11 and are then mirrored by currentmirrors Q12,Q13 and Q14,Q15 to another mirror Q16,Q17. The differencecurrent I_(COMP) is used to affect the bias of the detector, for exampleby applying I_(COMP) to a resistor ladder that is used in aninterpolator for an RMS detector having a multiplicity of squaringcells. The user can adjust the compensation by connecting resistors Rcpaand Rcpb to user-accessible terminals CPA and CPB. Any differencebetween the currents Icpa and Icpb causes a negative or positive tilt inthe temperature compensation. Trial-and-error techniques must be used todetermine values of Rcpa and Rcpb that provide an approximation of theamount of temperature compensation required for any particular operatingfrequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art temperature compensation circuit for anRF power detector.

FIG. 2 illustrates a prior art circuit used to generate the tail currentfor the circuit of FIG. 1.

FIG. 3 illustrates another prior art circuit used to generate the tailcurrent for the circuit of FIG. 1.

FIG. 4 illustrates another prior art temperature compensation circuitfor an RF power detector.

FIG. 5 illustrates an embodiment of a temperature compensation systemfor an RF power detector according to some of the inventive principlesof this patent disclosure.

FIG. 6 illustrates another embodiment of a temperature compensationsystem for an RF power detector according to some of the inventiveprinciples of this patent disclosure.

FIG. 7 illustrates another embodiment of a temperature compensationsystem for an RF power detector according to some of the inventiveprinciples of this patent disclosure.

FIG. 8 illustrates an example embodiment showing some possibleimplementation details of a slope circuit according to some of theinventive principles of this patent disclosure.

FIGS. 9-11 illustrate the operation of the circuit of FIG. 8 for variouscombinations of temperature dependent tail currents.

FIG. 12 illustrates another example embodiment showing some possibleimplementation details of a slope circuit according to some of theinventive principles of this patent disclosure.

FIG. 13 illustrates an example embodiment showing some possibleimplementation details of a bow circuit according to some of theinventive principles of this patent disclosure.

FIG. 14 illustrates the operation of the circuit of FIG. 13 for variousamounts of adjustment.

FIG. 15 illustrates an example embodiment of a circuit for providingadjustable tail current according to some of the inventive principles ofthis patent disclosure.

DETAILED DESCRIPTION

FIG. 5 illustrates an embodiment of a temperature compensation systemfor an RF power detector according to some of the inventive principlesof this patent disclosure. In the embodiment of FIG. 5, an integratedcircuit 10 includes an RF power detector 12 and a temperaturecompensation circuit 14 which provides temperature compensation to thedetector. A first function generator 16 provides a first-order componentto the temperature compensation, and a second function generator 18provides a second-order component to the temperature compensation. Thetwo components may be independently adjusted.

One approach to implementing the system of FIG. 5 according to some ofthe inventive principles of this patent disclosure involves identifyingthe temperature characteristics of a specific detector over a range ofoperating frequencies, and implementing the function generators tocreate an approximation of the specific frequency/temperaturecharacteristics of the detector. The approximation includes componentsfrom both of the function generators. In this context, the order of thefunction generator refers to the relative degree of precision (orcomplexity) the component adds to the approximation. For example, with azeroth-order approximation, a simple function is utilized (in someembodiments this can be as simple as a constant) to provide a roughorder of magnitude approximation. With a first order approximation, amore complex function is utilized to provide a more refined fit to theactual frequency/temperature characteristics of the detector. Higherorder approximations involve the use of temperature functions ofprogressively greater complexity and refinement.

Although first and second-order function generators are shown in theembodiment of FIG. 5, the inventive principles are not limited to thesespecific details. For example, any combination of two or more generatorshaving any orders (e.g., 0th, 1st, 2nd, etc.) can be used. The systemmay be arranged to enable the user to adjust the functions themselves,or to adjust the relative amount of the component that each functionprovides to the overall approximation.

Another approach to implementing the system of FIG. 5 according to someof the inventive principles of this patent disclosure involvesimplementing the function generators as predefined functions andenabling the user to adjust the relative amount of the component thateach function provides through trial-and-error or look-up table.

FIG. 6 illustrates another embodiment of a temperature compensationsystem according to some of the inventive principles of this patentdisclosure. In the embodiment of FIG. 6, individual temperaturecompensation signals S_(CMP0), S_(CMP1), S_(CMP2) . . . S_(CMPN) aregenerated separately and combined to create a combined compensationsignal S_(COMP) which can be used to provide temperature compensation toa detector. Each of the individual temperature compensation signals hasa corresponding order. For example the signal S_(CMP1), may have a firstorder temperature function, S_(CMP2) may have a second order temperaturefunction, etc.

In one example embodiment, the individual temperature compensationsignals may include terms that combine to form a polynomial. Forexample, the combined compensation signal may have the following form:

S _(COMP) =A ₀ +A ₁ T+A ₂ T ² + . . . +A _(N) T ^(N)   (Eq. 1)

where T is temperature (in ° K) and A₀, A₁ and A₂ are coefficients, anyor all of which can be made adjustable by the user. Thus, thecompensation signal has a constant component A₀, a linear component A₁Tand a nonlinear (or quadratic) component A₂T².

In another example embodiment, the individual terms may themselves bemore complex functions of temperature:

S _(COMP) =f ₁(T)+f ₂(T)+f ₂(T)+ . . . +f _(N)(T)   (Eq. 2)

where the functions f₁(T), f₂(T) and f₂(T) are progressively higherorder functions of temperature. For example, the functions maythemselves be polynomials, or then can be transcendental functions suchas exponentials, logarithms, etc. As with the embodiment of Eq. 1, anyor all of the terms can also include a coefficient that can be madeadjustable by the user.

FIG. 7 illustrates another embodiment of a temperature compensationsystem for an RF power detector according to some of the inventiveprinciples of this patent disclosure. An integrated circuit 20 includesa slope circuit 22 to generate a first compensation signal I_(CMP1)which varies linearly with temperature, and a bow circuit 24 to generatea second compensation signal I_(CMP2) which varies with the square oftemperature. The two individual compensation signals are combined tocreate a final compensation signal I_(COMP) which is applied to thedetector 26. User accessible terminals TCM1 and TCM2 enable the user toadjust the contributions of the I_(CMP1) and I_(CMP2) components toI_(COMP), respectively.

FIG. 8 illustrates an example embodiment showing some possibleimplementation details of the slope circuit 22 of FIG. 7 according tosome of the inventive principles of this patent disclosure. Referring toFIG. 8, diode connected transistors Q18 and Q19 are biased by currentsI₇ and I₈, respectively. The ΔV_(BE) developed across Q18 and Q19 isapplied to the inputs of dual multiplier cells Q20,Q21 and Q22,Q23,which are biased by tail currents I₉ and I₁₀, respectively. Anadjustment current I_(ADJ1) enables the user to adjust the relativecontribution from the two multipliers which have their outputs connectedtogether. The slope compensation signal is taken as the differencebetween the currents I_(SLP1) and I_(SLP2). Alternatively, the outputmay be made single-ended.

In one embodiment, the currents I₇ and I₈ are ZTAT currents. Thus, thediode connected transistors Q18 and Q19 do not contribute to thetemperature function and serve merely as pre-distortion diodes so thatmultiplier cells Q20,Q21 and Q22,Q23 operate as pure multipliers todetermine the relative amounts of I₉ and I₁₀ that are provided to theoutputs. The choice of temperature function selected for I₉ and I₁₀determine the direction and extent of the sloping temperaturecompensation provided by the circuit. For example, if one of thecurrents is made PTAT and the other is made ZTAT, the circuit provides arange of linear sloping outputs as shown in FIG. 9 where amount of slopeis determined by the value of I_(ADJ1). That is, as the value ofI_(ADJ1) is swept through its range, the tilt of the output functionrotates from a position flat on the horizontal axis to the maximum valueshown by the line I_(P).

If one of I₉ and I₁₀ is made CTAT and the other is made ZTAT, thecircuit provides a range of slopes in the opposite direction as shown inFIG. 10. If additional, bi-directional adjustment range is needed, thetail currents can be made PTAT and CTAT with the resulting full range ofnegative and positive tilt shown in FIG. 11.

FIG. 12 illustrates another example embodiment showing some possibleimplementation details of the slope circuit 22 of FIG. 7 according tosome of the inventive principles of this patent disclosure. Theembodiment of FIG. 12 is similar to that of FIG. 8, but the multipliercores are implemented with PNP transistors. A bias voltage generatorincluding Q26 is arranged to generate a bias voltage V_(B) to establishcurrents I₇ and I₈ in Q24 and Q25. The bias voltage V_(B) also serves asan anchor for cascode transistors Q27 and Q28. If I₇ and I₈ have thesame temperature function, the diode connected transistors Q18 and Q19do not contribute to the temperature function of the compensation signaland serve merely as pre-distortion diodes so that multiplier cellsQ20,Q21 and Q22,Q23 operate as pure multipliers to determine therelative amounts of I₉ and I₁₀ that are provided to the outputs. Thecurrents I₇ and I₈ are preferably made ZTAT as this simplifies theinterface for the user adjustment, I₇ and I₈ can be made CTAT, PTAT orany other function of temperature.

The adjustment current I_(ADJ1) is applied to the emitter terminal ofQ24 through R13 which is connected to user-accessible terminal TCM1. Areference voltage V_(REF) which is generated on the integrated circuitcan be brought out to another user-accessible terminal VREF to provide aconvenient voltage source to drive a voltage divider including R19 andR20 for creating the adjustment current.

The output of the slope circuit I_(CMP1) is taken from the collectors ofQ20 and Q22. The node ADD at the output of the multipliers provides aconvenient summing node for adding the nonlinear compensation currentI_(CMP2) from a bow circuit as described below. The final combinedoutput signal I_(COMP) can then be taken from the other side of cascodetransistor Q27. Transistor Q29 may be included to provide an additionaloffset to the output of the slope circuit.

FIG. 13 illustrates an example embodiment showing some possibleimplementation details of the bow circuit 22 of FIG. 7 according to someof the inventive principles of this patent disclosure. Referring to FIG.13, the junctions that provide the ΔV_(BE) input to the multiplier cellare arranged in stacks to generate second order functions, thusproviding a temperature function with bow (or curvature). In thisexample, I₁₁ and I₁₃ are made PTAT, while, I₁₄ and I₁₅ are made ZTAT.The currents are all scaled to have equal values (unit of current) atsome predetermined temperature, e.g., 300° K, except that I₁₂ is scaledtwice as large (made with two units). Current I₁₁ subtracts a PTATcurrent from the ZTAT current of I₁₂ to produce a CTAT current in Q30.Transistor Q31 is biased with a PTAT current, and Q33 and Q32 are bothbiased by ZTAT currents. Diode connected transistor QD and R21 elevatethe common emitter node of Q31 and Q32 above common COM.

The base-emitter voltages V_(BE) of Q30, Q31, Q32 and Q33 are asfollows:

$\begin{matrix}{V_{{BE}\; 30} = {V_{T}{\ln \left( \frac{I_{C}}{I_{S}} \right)}}} & \left( {{Eq}.\mspace{14mu} 3} \right) \\{V_{{BE}\; 31} = {V_{T}{\ln \left( \frac{I_{P}}{I_{S}} \right)}}} & \left( {{Eq}.\mspace{14mu} 4} \right) \\{V_{{BE}\; 32} = {V_{T}{\ln \left( \frac{I_{Z}}{I_{S}} \right)}}} & \left( {{Eq}.\mspace{14mu} 5} \right) \\{V_{{BE}\; 33} = {V_{T}{\ln \left( \frac{I_{Z}}{I_{S}} \right)}}} & \left( {{Eq}.\mspace{14mu} 6} \right)\end{matrix}$

where V_(T) is the thermal voltage kT/q, and I_(S) is the saturationcurrent for a bipolar junction transistor (BJT). The ΔV_(BE) across theemitters of Q30 and Q32 is:

ΔV _(BE) =V _(BE30) +V _(BE31) V _(BE32) −V _(BE33)   (Eq. 7)

Substituting Eqs. 3-6 into Eq. 7 and rearranging provides:

$\begin{matrix}{{\Delta \; V_{BE}} = {{V_{T}{\ln \left( \frac{I_{C}}{I_{S}} \right)}} + {V_{T}{\ln \left( \frac{I_{P}}{I_{S}} \right)}} - {V_{T}{\ln \left( \frac{I_{Z}}{I_{S}} \right)}} - {V_{T}{\ln \left( \frac{I_{Z}}{I_{S}} \right)}}}} & \left( {{Eq}.\mspace{14mu} 8} \right) \\{{\Delta \; V_{BE}} = {V_{T}{\ln\left( \frac{I_{C}I_{P}}{I_{Z}^{2}} \right)}}} & \left( {{Eq}.\mspace{14mu} 9} \right)\end{matrix}$

Substituting I_(C)=2I_(Z)−I_(P) yields:

$\begin{matrix}{{\Delta \; V_{BE}} = {V_{T}{\ln\left( \frac{{2I_{Z}I_{P}} - I_{P}^{2}}{I_{Z}^{2}} \right)}}} & \left( {{Eq}.\mspace{14mu} 10} \right)\end{matrix}$

The ΔV_(BE) is applied as the input Vi to the transconductance (gm)multiplier cell Q34,Q35 which is biased by an adjustable tail currentI₁₆. The transfer function of a generic gm cell has a hyperbolic tangent(tanh) form which may be stated a follows:

$\begin{matrix}{I_{OUT} = {I_{T}{\tanh \left( \frac{V_{i}}{2V_{T}} \right)}}} & \left( {{Eq}.\mspace{14mu} 11} \right)\end{matrix}$

where I_(T) is the bias or “tail” current through the gm cell and V_(i)is the differential input voltage. If Eq. 10 is substituted into Eq. 11,the V_(T)s cancel and the result is:

$\begin{matrix}{I_{OUT} = {I_{16}{\tanh\left( \frac{\ln \left\lbrack {\left( {{2I_{Z}I_{P}} - I_{P}^{2}} \right)/I_{Z}^{2}} \right\rbrack}{2} \right)}}} & \left( {{Eq}.\mspace{14mu} 12} \right)\end{matrix}$

If the input signal to the gm cell is kept relatively small, the tanhfunction may be approximated as simply the operand itself:

$\begin{matrix}{I_{OUT} \approx {I_{16}\left( \frac{\ln \left\lbrack {\left( {{2I_{Z}I_{P}} - I_{P}^{2}} \right)/I_{Z}^{2}} \right\rbrack}{2} \right)}} & \left( {{Eq}.\mspace{14mu} 13} \right)\end{matrix}$

In this example, the PTAT and ZTAT currents are scaled with equal units,so the magnitude of I_(Z) is roughly equal to the magnitude of I_(P),and therefore, the operand of the In function is always close to one.However, if the operand of a natural logarithmic function is close toone, the function may be approximated as simply the operand itself,minus one (i.e., ln(a)≈a−1 when a≈1). Therefore:

$\begin{matrix}{I_{OUT} \approx {I_{16}\left( \frac{{\left( {{2I_{Z}I_{P}} - I_{P}^{2}} \right)/I_{Z}^{2}} - 1}{2} \right)}} & \left( {{Eq}.\mspace{14mu} 14} \right)\end{matrix}$

From Eq. 14 it is apparent that the output has a second ordertemperature dependency due to the −I_(P) ² term. The multiplier cellQ34,Q35 is loaded by a current mirror 28, and the output compensationcurrent I_(CMP2) is taken as the difference of the collector currents inQ34 and Q35.

The amount (or weighting) of the output from the bow circuit of FIG. 13can be adjusted by adjusting the tail current I₁₆ to provide a range ofoutputs as shown in FIG. 14.

To provide a zeroth-order offset, a ZTAT current I₁₈ can be added toI_(CMP2). This combined “bow plus offset” current can be applied to theADD terminal of FIG. 9 through a cascode transistor Q38 to provide thecombined temperature compensation signal I_(COMP) as discussed above.

In other embodiments, the multiplicity of junctions and temperatureshaped bias currents may be configured in other arrangements to provideany other suitable function of temperature. Moreover, the multiplicitycan be arranged to provide temperature functions of any order. In theexample of FIG. 13, the junctions are arranged in stacks of two toprovide second-order functions. But they can also be arranged in stacksof three to provide third-order functions, and so on, or they can bemixed to provide other functions.

FIG. 15 illustrates an example embodiment of a circuit for providing theadjustable tail current I₁₆ to the bow circuit of FIG. 13 according tosome of the inventive principles of this patent disclosure. Auser-applied adjustment voltage on the terminal TCM2 is compared to areference voltage V_(REF) by a differential pair of transistors Q36,Q37which splits a tail current I₁₇ between a power supply common COM, and acurrent mirror 30. The current mirror provides the adjustable tailcurrent I₁₆ to the multiplier of FIG. 13. If I₁₇ is made ZTAT, noadditional temperature shaping is provided I₁₆, and the temperatureshaping of the output current I_(CMP2) of the bow circuit is determinedsolely by the ΔV_(BE) applied to the Vi input of the multiplier.Alternatively, the current I₁₇ can be a temperature dependent current(e.g., PTAT or CTAT) to provide additional temperature shaping.

Referring again to FIG. 7, when the slope and bow circuits areimplemented as shown in the examples above and their outputs arecombined to generate the final compensation signal I_(COMP), theresulting system provides highly flexible and customizable compensationthat can be adjusted by the user to provide an accurate approximation ofthe temperature and frequency characteristics of the detector. Theuser-accessible terminals enable the user to create a compositecompensation signal having any suitable amounts of the temperatureshapes shown in FIGS. 9-11 and 14.

The inventive principles of this patent disclosure have been describedabove with reference to some specific example embodiments, but theseembodiments can be modified in arrangement and detail without departingfrom the inventive concepts. For example, the embodiments describedabove with respect to FIGS. 5 and 7-16 have been shown in the context ofa system having two function generators (one first order and anothersecond order) and two user accessible terminals. As is apparent fromFIG. 6, however, the inventive principles of this patent disclosureenable the creation of compensation systems involving the generation ofany number of temperature functions of any varying orders, and anynumber of user accessible terminals. For example, the embodiment of FIG.5 may be implemented with only one terminal to adjust one of thefunctions. Or the embodiment of FIG. 13 may be provided with anotheruser-accessible terminal to adjust I₁₈. Other embodiments may includethird-order, fourth-order, etc. function generators, alone or incombination with additional zeroth, first and second-order generators,and any number of user-accessible terminals may be provided to adjustwhichever functions are beneficial to adjust. A temperature function ofa certain order may also include components of lower order functions.For example, the function generated by the embodiment of FIG. 13 is asecond-order function even though it includes first and zeroth-ordercomponents.

A user-accessible terminal can be accessed by whatever technique wouldnormally be used by a user of the device. Thus, if the product is soldas a die, the user-accessible terminals may be bond-pads like any of theother terminals. If the die is packaged, a user accessible terminal maybe a pin, lead or other type of contact like any of the other terminalson the package.

A compensation signal according to the inventive principles of thispatent disclosure can be applied to the detector in any suitable manner.For example, the combined compensation signal I_(COMP) shown in FIG. 12can be added into the setpoint interface of an RMS detector through aresistive, or it can be added to the output of a log amp through one ormore summing nodes. The compensation circuit can be separate from, orintegral with, the detector. The compensation circuit may be fabricatedon a separate integrated circuit from the detector and packaged in aseparate package or in the same package as the detector, or mounted onthe same header as the detector. An adjustment signal may be applied toa compensation circuit only to vary the amount of compensation, or theadjustment may contribute additional functionality to the compensation,as for example, if the adjustment signal is a PTAT or CTAT signal.

As further examples, some transistors have been illustrated as bipolarjunction transistors (BJTs) of specific polarities, but MOS and othertypes and polarities of devices may be used as well. Thus, the termsbase, emitter and collector are understood to refer to the correspondingterminals of other types of transistors. Likewise, in FIG. 8, currentsI₇ and I₈, can be implemented as PTAT, CTAT or other temperaturedependent currents to provide additional temperature shaping.

Since the embodiments described above can be modified in arrangement anddetail without departing from the inventive concepts, such changes andmodifications are considered to fall within the scope of the followingclaims.

1. An integrated circuit comprising: an RF power detector having aninput to receive an RF signal and an output to provide a signalrepresentative of the power of the RF signal; a temperature compensationcircuit coupled to the RF power detector to provide temperaturecompensation to the RF power detector; a first user-accessible terminalto adjust a first component of the temperature compensation; and asecond user-accessible terminal to adjust a second component of thetemperature compensation; wherein the first and second components are ofdifferent orders.
 2. The integrated circuit of claim 1 wherein: thefirst component of the temperature compensation comprises a first-ordercomponent; and the second component of the temperature compensationcomprises a second-order component.
 3. The integrated circuit of claim 2wherein: the first-order component comprises a linear component; and thesecond-order component comprises a quadratic component.
 4. Theintegrated circuit of claim 1 wherein the first and second componentsmay be adjusted independently.
 5. A system comprising: an RF powerdetector having an input to receive an RF signal and an output toprovide a signal representative of the power of the RF signal; and atemperature compensation circuit coupled to the RF power detector toprovide temperature compensation to the RF power detector, wherein thetemperature compensation circuit comprises: a first function generatorto generate a first compensation signal having a first temperaturefunction; and a second function generator to generate a secondcompensation signal having a second temperature function having adifferent order than the first temperature function.
 6. The system ofclaim 5 further comprising a first user-accessible terminal to enable toadjust the first component of the temperature compensation.
 7. Thesystem of claim 6 further comprising a second user-accessible terminalto enable to adjust the second component of the temperaturecompensation.
 8. The system of claim 5 wherein the first functiongenerator comprises: a ΔV_(BE) cell to generate a ΔV_(BE) signal; and afirst multiplier to multiply the ΔV_(BE) signal by a first temperaturedependent signal.
 9. The system of claim 8 wherein the first functiongenerator further comprises a second multiplier to multiply the ΔV_(BE)signal by a second temperature dependent signal.
 10. The system of claim5 wherein each of the first and second temperature dependent signalscomprise one of a PTAT, ZTAT or CTAT signal.
 11. The system of claim 5wherein the detector and compensation circuit are fabricated on the sameintegrated circuit.
 12. The system of claim 5 wherein the detector andcompensation circuit are fabricated on the different integratedcircuits.
 13. The system of claim 5 wherein the second functiongenerator comprises: a ΔV_(BE) cell to generate a ΔV_(BE) signal havinga second-order temperature dependency; and a multiplier to multiply theΔV_(BE) signal by an adjustment signal.
 14. A method of temperaturecompensating an RF detector comprising: generating a first temperaturecompensation signal; generating a second temperature compensation signalhaving a different order than the first temperature compensation signal;combining the first and second temperature compensation signals togenerate a combined temperature compensation signal; and applying thecombined temperature compensation signal to the RF power detector. 15.The method of claim 14 further comprising independently adjusting thefirst and second temperature compensation signals.
 16. The method ofclaim 14 further comprising: generating a third temperature compensationsignal; and combining the third temperature compensation signal with thefirst and second temperature compensation signals to generate thecombined temperature compensation signal.
 17. The method of claim 14wherein: the first temperature compensation signal comprises afirst-order component; and the second temperature compensation signalcomprises a second-order component.
 18. The method of claim 17 whereinthe first-order component comprises a linear component.
 19. The methodof claim 18 wherein the second-order component comprises a quadraticcomponent.
 20. The method of claim 19 wherein the second-order componentcomprises a transcendental component.
 21. The method of claim 14 wherethe combined temperature compensation signal has the formS_(COMP)=A₀+A₁T+A₂T²A+ . . . +A_(N)T^(N) where T represents temperature.22. The method of claim 14 where the combined temperature compensationsignal has the form S_(COMP)=f₁(T)+f₂(T)+f₂(T)+ . . . +f_(N)(T) where Trepresents temperature.